Fukushima Nuclear Accident – a simple and accurate explanation

Editors’ Note: this post was written by a person who knew of nuclear physics but was not a nuclear engineer nor physicist, but an economist. This content has now been edited for accuracy by the MIT scientific community. Below is an updated version of the original post written by Josef Oehmen.

This post originally appeared on Morgsatlarge. Members of the NSE community have edited the original post and will be monitoring and posting comments, updates, and new information. Please visit to learn more. ***Note that the title of the original blog does not reflect the views of the authors of the site. The authors have been monitoring the situation, and are presenting facts on the situation as they develop. The original article was adopted as the authors believed it provided a good starting point to provide a summary background on the events at the Fukushima plant.***

The original post written by Dr Josef Oehmen “Why I am not worried about Japan’snuclear reactors.” are being reposted in different languages. They have not been checked / verified.

We will have to cover some fundamentals, before we get into what is going on.

Construction of the Fukushima nuclear power plants

The plants at Fukushima are Boiling Water Reactors (BWR for short). A BWR produces electricity by boiling water, and spinning a a turbine with that steam. The nuclear fuel heats water, the water boils and creates steam, the steam then drives turbines that create the electricity, and the steam is then cooled and condensed back to water, and the water returns to be heated by the nuclear fuel. The reactor operates at about 285 °C.

Welcome to The Energy Collective

We are an independent, member-driven community of energy and climate study professionals. Our member-bloggers are providing ongoing analysis of events unfolding in Japan.

The nuclear fuel is uranium oxide. Uranium oxide is a ceramic with a very high melting point of about 2800 °C. The fuel is manufactured in pellets (cylinders that are about 1 cm tall and 1 com in diameter). These pellets are then put into a long tube made of Zircaloy (an alloy of zirconium) with a failure temperature of 1200 °C (caused by the auto-catalytic oxidation of water), and sealed tight. This tube is called a fuel rod. These fuel rods are then put together to form assemblies, of which several hundred make up the reactor core.

The solid fuel pellet (a ceramic oxide matrix) is the first barrier that retains many of the radioactive fission products produced by the fission process. The Zircaloy casing is the second barrier to release that separates the radioactive fuel from the rest of the reactor.

The core is then placed in the pressure vessel. The pressure vessel is a thick steel vessel that operates at a pressure of about 7 MPa (~1000 psi), and is designed to withstand the high pressures that may occur during an accident. The pressure vessel is the third barrier to radioactive material release.

The entire primary loop of the nuclear reactor – the pressure vessel, pipes, and pumps that contain the coolant (water) – are housed in the containment structure. This structure is the fourth barrier to radioactive material release. The containment structure is a hermetically (air tight) sealed, very thick structure made of steel and concrete. This structure is designed, built and tested for one single purpose: To contain, indefinitely, a complete core meltdown. To aid in this purpose, a large, thick concrete structure is poured around the containment structure and is referred to as the secondary containment.

Both the main containment structure and the secondary containment structure are housed in the reactor building. The reactor building is an outer shell that is supposed to keep the weather out, but nothing in. (this is the part that was damaged in the explosions, but more to that later).

Fundamentals of nuclear reactions

The uranium fuel generates heat by neutron-induced nuclear fission. Uranium atoms are split into lighter atoms (aka fission products). This process generates heat and more neutrons (one of the particles that forms an atom). When one of these neutrons hits another uranium atom, that atom can split, generating more neutrons and so on. That is called the nuclear chain reaction. During normal, full-power operation, the neutron population in a core is stable (remains the same) and the reactor is in a critical state.

It is worth mentioning at this point that the nuclear fuel in a reactor can never cause a nuclear explosion like a nuclear bomb. At Chernobyl, the explosion was caused by excessive pressure buildup, hydrogen explosion and rupture of all structures, propelling molten core material into the environment. Note that Chernobyl did not have a containment structure as a barrier to the environment. Why that did not and will not happen in Japan, is discussed further below.

In order to control the nuclear chain reaction, the reactor operators use control rods. The control rods are made of boron which absorbs neutrons. During normal operation in a BWR, the control rods are used to maintain the chain reaction at a critical state. The control rods are also used to shut the reactor down from 100% power to about 7% power (residual or decay heat).

The residual heat is caused from the radioactive decay of fission products. Radioactive decay is the process by which the fission products stabilize themselves by emitting energy in the form of small particles (alpha, beta, gamma, neutron, etc.). There is a multitude of fission products that are produced in a reactor, including cesium and iodine. This residual heat decreases over time after the reactor is shutdown, and must be removed by cooling systems to prevent the fuel rod from overheating and failing as a barrier to radioactive release. Maintaining enough cooling to remove the decay heat in the reactor is the main challenge in the affected reactors in Japan right now.

It is important to note that many of these fission products decay (produce heat) extremely quickly, and become harmless by the time you spell “R-A-D-I-O-N-U-C-L-I-D-E.” Others decay more slowly, like some cesium, iodine, strontium, and argon.

What happened at Fukushima (as of March 12, 2011)

The following is a summary of the main facts. The earthquake that hit Japan was several times more powerful than the worst earthquake the nuclear power plant was built for (the Richter scale works logarithmically; for example the difference between an 8.2 and the 8.9 that happened is 5 times, not 0.7).

When the earthquake hit, the nuclear reactors all automatically shutdown. Within seconds after the earthquake started, the control rods had been inserted into the core and the nuclear chain reaction stopped. At this point, the cooling system has to carry away the residual heat, about 7% of the full power heat load under normal operating conditions.

The earthquake destroyed the external power supply of the nuclear reactor. This is a challenging accident for a nuclear power plant, and is referred to as a “loss of offsite power.” The reactor and its backup systems are designed to handle this type of accident by including backup power systems to keep the coolant pumps working. Furthermore, since the power plant had been shut down, it cannot produce any electricity by itself.

For the first hour, the first set of multiple emergency diesel power generators started and provided the electricity that was needed. However, when the tsunami arrived (a very rare and larger than anticipated tsunami) it flooded the diesel generators, causing them to fail.

One of the fundamental tenets of nuclear power plant design is “Defense in Depth.” This approach leads engineers to design a plant that can withstand severe catastrophes, even when several systems fail. A large tsunami that disables all the diesel generators at once is such a scenario, but the tsunami of March 11th was beyond all expectations. To mitigate such an event, engineers designed an extra line of defense by putting everything into the containment structure (see above), that is designed to contain everything inside the structure.

When the diesel generators failed after the tsunami, the reactor operators switched to emergency battery power. The batteries were designed as one of the backup systems to provide power for cooling the core for 8 hours. And they did.

After 8 hours, the batteries ran out, and the residual heat could not be carried away any more. At this point the plant operators begin to follow emergency procedures that are in place for a “loss of cooling event.” These are procedural steps following the “Depth in Defense” approach. All of this, however shocking it seems to us, is part of the day-to-day training you go through as an operator.

At this time people started talking about the possibility of core meltdown, because if cooling cannot be restored, the core will eventually melt (after several days), and will likely be contained in the containment. Note that the term “meltdown” has a vague definition. “Fuel failure” is a better term to describe the failure of the fuel rod barrier (Zircaloy). This will occur before the fuel melts, and results from mechanical, chemical, or thermal failures (too much pressure, too much oxidation, or too hot).

However, melting was a long ways from happening and at this time, the primary goal was to manage the core while it was heating up, while ensuring that the fuel cladding remain intact and operational for as long as possible.

Because cooling the core is a priority, the reactor has a number of independent and diverse cooling systems (the reactor water cleanup system, the decay heat removal, the reactor core isolating cooling, the standby liquid cooling system, and others that make up the emergency core cooling system). Which one(s) failed when or did not fail is not clear at this point in time.

Since the operators lost most of their cooling capabilities due to the loss of power, they had to use whatever cooling system capacity they had to get rid of as much heat as possible. But as long as the heat production exceeds the heat removal capacity, the pressure starts increasing as more water boils into steam. The priority now is to maintain the integrity of the fuel rods by keeping the temperature below 1200°C, as well as keeping the pressure at a manageable level. In order to maintain the pressure of the system at a manageable level, steam (and other gases present in the reactor) have to be released from time to time. This process is important during an accident so the pressure does not exceed what the components can handle, so the reactor pressure vessel and the containment structure are designed with several pressure relief valves. So to protect the integrity of the vessel and containment, the operators started venting steam from time to time to control the pressure.

As mentioned previously, steam and other gases are vented. Some of these gases are radioactive fission products, but they exist in small quantities. Therefore, when the operators started venting the system, some radioactive gases were released to the environment in a controlled manner (ie in small quantities through filters and scrubbers). While some of these gases are radioactive, they did not pose a significant risk to public safety to even the workers on site. This procedure is justified as its consequences are very low, especially when compared to the potential consequences of not venting and risking the containment structures’ integrity.

During this time, mobile generators were transported to the site and some power was restored. However, more water was boiling off and being vented than was being added to the reactor, thus decreasing the cooling ability of the remaining cooling systems. At some stage during this venting process, the water level may have dropped below the top of the fuel rods. Regardless, the temperature of some of the fuel rod cladding exceeded 1200 °C, initiating a reaction between the Zircaloy and water. This oxidizing reaction produces hydrogen gas, which mixes with the gas-steam mixture being vented. This is a known and anticipated process, but the amount of hydrogen gas produced was unknown because the operators didn’t know the exact temperature of the fuel rods or the water level. Since hydrogen gas is extremely combustible, when enough hydrogen gas is mixed with air, it reacts with oxygen. If there is enough hydrogen gas, it will react rapidly, producing an explosion. At some point during the venting process enough hydrogen gas built up inside the containment (there is no air in the containment), so when it was vented to the air an explosion occurred. The explosion took place outside of the containment, but inside and around the reactor building (which has no safety function). Note that a subsequent and similar explosion occurred at the Unit 3 reactor. This explosion destroyed the top and some of the sides of the reactor building, but did not damage the containment structure or the pressure vessel. While this was not an anticipated event, it happened outside the containment and did not pose a risk to the plant’s safety structures.

Since some of the fuel rod cladding exceeded 1200 °C, some fuel damage occurred. The nuclear material itself was still intact, but the surrounding Zircaloy shell had started failing. At this time, some of the radioactive fission products (cesium, iodine, etc.) started to mix with the water and steam. It was reported that a small amount of cesium and iodine was measured in the steam that was released into the atmosphere.

Since the reactor’s cooling capability was limited, and the water inventory in the reactor was decreasing, engineers decided to inject sea water (mixed with boric acid – a neutron absorber) to ensure the rods remain covered with water. Although the reactor had been shut down, boric acid is added as a conservative measure to ensure the reactor stays shut down. Boric acid is also capable of trapping some of the remaining iodine in the water so that it cannot escape, however this trapping is not the primary function of the boric acid.

The water used in the cooling system is purified, demineralized water. The reason to use pure water is to limit the corrosion potential of the coolant water during normal operation. Injecting seawater will require more cleanup after the event, but provided cooling at the time.

This process decreased the temperature of the fuel rods to a non-damaging level. Because the reactor had been shut down a long time ago, the decay heat had decreased to a significantly lower level, so the pressure in the plant stabilized, and venting was no longer required.

***UPDATE – 3/14 8:15 pm EST***

Units 1 and 3 are currently in a stable condition according to TEPCO press releases, but the extent of the fuel damage is unknown. That said, radiation levels at the Fukushima plant have fallen to 231 micro sieverts (23.1 millirem) as of 2:30 pm March 14th (local time).

***UPDATE – 3/14 10:55 pm EST***

The details about what happened at the Unit 2 reactor are still being determined. The post on what is happening at the Unit 2 reactor contains more up-to-date information. Radiation levels have increased, but to what level remains unknown.

I think this one passage sums up the breathtakingly broad apologist sweep of this article:

“A very small amount of Cesium was released, as well as Iodine. … The Cesium and Iodine isotopes were carried out to the sea and will never be seen again.”

Oh, sure!

Just dump stuff into the oceans!

You’ll never see it again!

Excuse me?

Did you just arrive here from the 1950’s?

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MSci

March 13, 2011 18:48

Also I have to object in the strongest possible terms to the following statement:

“Japan is looking at an INES Level 4 Accident: Nuclear accident with local consequences. That is bad for the company that owns the plant, but not for anyone else.”

200.000 people in emergeny evacuee camps. This is again as many as the earthquake/tsunami refuigees, which have already started to go home and rebuild. Many of the 200.000 will not be able to go home for some time. Some may never be able to return.

I say: into a plane with him and dump him at Fukushima. They need every hand they can get, and as an “expert´” who knows it’s “safe” now, I think Oehmen will be welcome.

But no. Better to cower under your 10000-bucks MIT research desk mouthfarting lies. That’s the “courage” of these dregs of humanity.

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Bob Miller

March 13, 2011 18:55

Very good article, but for a PhD scientist at MIT one would expect that Dr Oehmen would know that the difference between a magnitude 8.2 and 8.9 earthquake would be 5 times, and not 7.

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Piotr

March 13, 2011 19:02

Great read. Clear and detailed explanation that puts some proportion to the problems. Most appreciate your work Barry. Thanks!

@Rick: US & Russia both most advanced technological societies? Please take a trip to Russia (or read)

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Will

March 13, 2011 19:34

Good technical information. I really appreciate the systematic explanation and dampening of hysteria. But, at the same time, sanguine about the threat we faced. There were multiple levels of safety, which is a baseline. But it was designed for an 8.0 earthquake — and missed that by a magnitude of 7. Several safety systems failed. The designers and engineers should be congratulated for handling it. But that misses the point. Studies of disasters show that they are unpredictable. Systems fail. O rings errode. Bridge moorings get fatigued. Thats bad. But when nuclear systems fail, we could be looking at devastation on an unequaled scale. Its a risk calculus that does not add up for me. Everything works fine until it doesn’t, and when disasters hit and systems fail, the costs could be catastrophic and persistent on a time scale past humans’ lietimes.

The third bullet point says “the cesium and iodine isotopes were carried out to see, never to be seen again.” By humans. They are in the ecology. This dismissal of impacts on the ecology is what makes me distrust the analysis of the safety of nuclear power. We act as if humans are self contained and the only metric. Its as if the analysis’ criteria is “Did any humans drop dead on the spot? No? Whew. All clear.” We’re in a living system, folks, with all of the elements interconnected. There is no “away” for things to go to where they will not impact us and the ecology.

So, really appreciate the clear knowledge and work here. But needed to respond to the way you implicitly frame the wider implications.

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Kim2

March 13, 2011 19:56

Excellent article – one of the best I’ve read. I didn’t have a detailed knowledge of the plumbing of a reactor until now, although as a former particle physicist I do understand fission (and have a fairly good understanding of the General Theory too !!).

Those pointing to the author’s alleged “callousness” should understand that none of this is desirable – quite the reverse – but on all the evidence to date it is NOT a catastrophe yet, and is most unlikely to become one.

As someone who spent half his life in Japan, and love the people and the place, I find nothing offensive in its tone whatsoever. And if it helps dispel some of the (natural but unwarranted) fear of those living in the shadow of these events, it will do much good.

I find this article by ” … Dr Josef Oehmen, a research scientist at MIT, in Boston. He is a PhD Scientist, whose father** has extensive experience in Germany’s nuclear industry … ” rather non scientific*** and pro-nuclear and evenly tendentious.

That fact together with the huge and yet unsolved problem of dealing with nuclear waste makes me very sceptical at this moment and opposed nuclear power as mainstream generator of electricity.

I am not against research into nuclear power or the production of Isotopes used in radiation therapy!

Last but not least the CO2 footprint of nuclear power is signigficant as the mining of fuel and the production and transport of yellow cake together with the efforts to deal with nuclear waste bring along a significant CO2 emission.

Again: Discussion and research is good, but facts are facts no matter how iterpretations might like to alter those facts into pro- AND con- statements… 🙂

Fact is there are problems now at Fukushima 1 and 2 powerplants and there is no clear status of being ‘in control’ .

Press Release (Mar 13,2011) Occurrence of a Specific Incident Stipulated in Article 15, Clause 1 of the Act on Special Measures Concerning Nuclear Emergency Preparedness (Extraordinary increase of radiation dose at site boundary)

At 2:48PM on March 11th, turbines and reactors of Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Station Unit 1 (Boiling Water Reactor, rated output 460 Megawatts) and Units 2 and 3 (Boiling Water Reactor, Rated Output 784 Megawatts) that had been operating at rated power automatically shutdown due to the Miyagiken-oki Earthquake.

After the shut down, the values of radioactive materials (iodine, etc) measured by the monitoring car have been increasing. Increase in the measured value has also been recognized in one of the monitoring posts.

Furthermore, at 3:29PM, Mar 12, radiation dose measured at site boundary has exceeded the limiting value. Therefore, at 4:17PM, Mar 12, it was determined that a specific incident stipulated in article 15, clause 1 has occurred.

(as per the previous press release)

After that, the radiation dose at the monitoring post decreased once.Today, the measured value revamped and the radiation dose measured atsite boundary exceeded the limiting value again. As such, at 8:56AM,today, it was determined that a specific incident stipulated in article15, clause 1 occurred.

We will endeavor to secure the safety and alongside, continue monitoring the environment of the site periphery.

All 6 units of Fukushima Daiichi Nuclear Power Station have been shut down.

[There is no update from the previous press release.]

Unit 1(Shut down)- Reactor has been shut down. However, the unit is under inspection due to the explosive sound and white smoke that was confirmed after the big quake occurred at 3:36PM. - We have been injecting sea water and boric acid which absorbs neutron into the reactor pressure vessel.

Unit 2(Shut down)- Reactor has been shut down and Reactor Core Isolation Cooling System has been injecting water to the reactor. Current reactor water level is lower than normal level, but the water level is steady. After fully securing safety, measures to lowering the pressure of reactor containment vessel has been taken, under the instruction of the national government.

Unit 3(Shut down)- Reactor has been shut down. However, as High Pressure Core Injection System has been automatically shut down and water injection to the reactor was interrupted, following the instruction by the government and with fully securing safety, steps to lowering the pressure of reactor containment vessel has been taken. Spraying in order to lower pressure level within the reactor containment vessel has been cancelled.- After that, safety relief valve has been opened manually, lowering the pressure level of the reactor, which was immediately followed by injection of boric acid water which absorbs neutron, into the reactor pressure vessel.

Unit 4 (shut down due to regular inspection)- Reactor has been shut down and sufficient level of reactor coolant to ensure safety is maintained.- Currently, we do not believe there is any reactor coolant leakage inside the reactor containment vessel.

Unit 5 (outage due to regular inspection)- Reactor has been shut down and sufficient level of reactor coolant to ensure safety is maintained.- Currently, we do not believe there is any reactor coolant leakage inside the reactor containment vessel.

Unit 6 (outage due to regular inspection)- Reactor has been shut down and sufficient level of reactor coolant to ensure safety is maintained.- Currently, we do not believe there is any reactor coolant leakage inside the reactor containment vessel.

Casualty- 2 workers of cooperative firm were injured at the occurrence of the earthquake, and were transported to the hospital.- 1 TEPCO employee who was not able to stand by his own with his hand holding left chest was transported to the hospital by an ambulance.- 1 subcontract worker at important earthquake-proof building was unconscious and transported to the hospital by an ambulance.- The radiation exposure of 1 TEPCO employee, who was working inside the reactor building, exceeded 100mSv and was transported to the hospital.- 2 TEPCO employees felt bad during their operation in the central control rooms of Unit 1 and 2 while wearing full masks, and were transferred to Fukushima Daini Power Station for consultation with a medical advisor.- 4 workers were injured and transported to the hospital after explosive sound and white smoke were confirmed around the Unit 1.- Presence of 2 TEPCO employees at the site are not confirmed

Others- We are currently coordinating with the relevant authorities and departments as to how to secure the cooling water to cool down the water in the spent nuclear fuel pool.- We measured radioactive materials inside of the nuclear power station area (outdoor) by monitoring car and confirmed that radioactive materials level is higher than ordinary level. Also, the level at monitoring post is higher than ordinary level. We will continue to monitor in detail the possibility of radioactive material being discharged from exhaust stack or discharge canal. The national government has instructed evacuation for those local residents within 20km radius of the periphery because it's possible that radioactive materials are discharged.

- We will continue to take all measures to restore the security of the site and to monitor the environment of the site periphery.

All 6 units of Fukushima Daiichi Nuclear Power Station have been shut down.

[There is no update from the previous press release.]

Unit 1(Shut down)- Reactor has been shut down. However, the unit is under inspection due to the explosive sound and white smoke that was confirmed after the big quake occurred at 3:36PM. - We have been injecting sea water and boric acid which absorbs neutron into the reactor pressure vessel.

Unit 2(Shut down)- Reactor has been shut down and Reactor Core Isolation Cooling System has been injecting water to the reactor. Current reactor water level is lower than normal level, but the water level is steady. After fully securing safety, measures to lowering the pressure of reactor containment vessel has been taken, under the instruction of the national government.

Unit 3(Shut down)- Reactor has been shut down. However, as High Pressure Core Injection System has been automatically shut down and water injection to the reactor was interrupted, following the instruction by the government and with fully securing safety, steps to lowering the pressure of reactor containment vessel has been taken. Spraying in order to lower pressure level within the reactor containment vessel has been cancelled.- After that, safety relief valve has been opened manually, lowering the pressure level of the reactor, which was immediately followed by injection of boric acid water which absorbs neutron, into the reactor pressure vessel.

Unit 4 (shut down due to regular inspection)- Reactor has been shut down and sufficient level of reactor coolant to ensure safety is maintained.- Currently, we do not believe there is any reactor coolant leakage inside the reactor containment vessel.

Unit 5 (outage due to regular inspection)- Reactor has been shut down and sufficient level of reactor coolant to ensure safety is maintained.- Currently, we do not believe there is any reactor coolant leakage inside the reactor containment vessel.

Unit 6 (outage due to regular inspection)- Reactor has been shut down and sufficient level of reactor coolant to ensure safety is maintained.- Currently, we do not believe there is any reactor coolant leakage inside the reactor containment vessel.

Casualty- 2 workers of cooperative firm were injured at the occurrence of the earthquake, and were transported to the hospital.- 1 TEPCO employee who was not able to stand by his own with his hand holding left chest was transported to the hospital by an ambulance.- 1 subcontract worker at important earthquake-proof building was unconscious and transported to the hospital by an ambulance.- The radiation exposure of 1 TEPCO employee, who was working inside the reactor building, exceeded 100mSv and was transported to the hospital.- 2 TEPCO employees felt bad during their operation in the central control rooms of Unit 1 and 2 while wearing full masks, and were transferred to Fukushima Daini Power Station for consultation with a medical advisor.- 4 workers were injured and transported to the hospital after explosive sound and white smoke were confirmed around the Unit 1.- Presence of 2 TEPCO employees at the site are not confirmed

Others- We are currently coordinating with the relevant authorities and departments as to how to secure the cooling water to cool down the water in the spent nuclear fuel pool.- We measured radioactive materials inside of the nuclear power station area (outdoor) by monitoring car and confirmed that radioactive materials level is higher than ordinary level. Also, the level at monitoring post is higher than ordinary level. We will continue to monitor in detail the possibility of radioactive material being discharged from exhaust stack or discharge canal. The national government has instructed evacuation for those local residents within 20km radius of the periphery because it's possible that radioactive materials are discharged.

- We will continue to take all measures to restore the security of the site and to monitor the environment of the site periphery.

the third

The value of radioactive material (iodine, etc) is increasing according to the monitoring car at the site (outside)

Below is major impact to TEPCO's facilities due to the Miyagiken-Oki Earthquake that occurred yesterday at 2:46PM.*new items are underlined

[Nuclear Power Station]Fukushima Daiichi Nuclear Power Station: Units 1 to 3: shutdown due to earthquake Units 4 to 6: outage due to regular inspection* The national government has instructed evacuation for those local residents within 20km radius of the site periphery.* The value of radioactive material (iodine, etc) is increasing according to the monitoring car at the site (outside).* Since the amount of radiation at the boundary of the site exceeds the limits, we decide at 4:17PM, Mar 12 and we have reported and/or noticed the government agencies concerned to apply the clause 1 of the Article 15 of the Radiation Disaster Measure at 5PM, Mar 12. The radiation dose at the monitoring post decreased once. Today, the measured value revamped and the radiation dose measured at site boundary exceeded the limiting value again. As such, at 8:56AM, today, it was determined that a specific incident stipulated in article 15, clause 1 occurred and at 09:01AM, today, notified accordingly.After that, the measured value by the monitoring car decreased once, however the value revamped and the radiation dose measured at site boundary exceeded the limitation again. As such, at 2:15PM, today, it was determined that a specific incident stipulated in article 15, clause 1 occurred and at 02:23PM, today, notified accordingly.* In addition, a vertical earthquake hit the site and big explosion has happened near the Unit 1 and smoke breaks out around 3:36PM, Mar 12th.* Unit 1: We started injection of sea water into the reactor core at 8:20PM, Mar 12 and then boric acid subsequently. We are coordinating with the relevant authorities and departments as to how to cool down water in the spent nuclear fuel pool.* Unit 2: Reactor has been shut down and Reactor Core Isolation Cooling System has been injecting water to the reactor. Current reactor water level is lower than normal level, but the water level is steady. After fully securing safety, we are preparing to implement a measure to reduce the pressure of the reactor containment vessels under the instruction of the national government. To do so, we operated the vent valve and completed the operation at 11:00AM, Mar 13.* Unit 3: High Pressure Coolant Injection System automatically stopped. We endeavored to restart the Reactor Core Isolation Cooling System but failed. Also, we could not confirm the water inflow of Emergency Core Cooling System. As such, we decided at 5.10AM, Mar 12, and we reported and/or noticed the government agencies concerned to apply the clause 1 of the Article 15 of the Radiation Disaster Measure at 5:58AM, Mar 13.In order to fully secure safety, we operated the vent valve to reduce the pressure of the reactor containment vessels (partial release of air containing radioactive materials) and completed the procedure at 8:41AM, Mar 13 (successfully completed at 09:20AM, Mar 13. After that, we began injecting water containing boric acid that absorbs neutron into the reactor by the fire pump from 09:25AM, Mar 13.Taking account of the situation that the water level within the pressure vessel did not rise for a long time and the radiation dose is increasing, we cannot exclude the possibility that the same situation occurred at Unit 1 on Mar 12 will occur. We are considering the countermeasure to prevent that.* We continue endeavoring to secure the safety that all we can do and monitoring the periphery.

Fukushima Daini Nuclear Power Station: Units 1 to 4: shutdown due to earthquake* The national government has instructed evacuation for those local residents within 10km radius of the periphery.* At present, we have decided to prepare implementing measures to reduce the pressure of the reactor containment vessel (partial discharge of air containing radioactive materials) in order to fully secure safety.These measures are considered to be implemented in Units 1, 2 and 3 and accordingly, we have reported and/or noticed the government agencies concerned. * Unit 3 has been stopped and being "nuclear reactor cooling hot stop" at 12:15PM.* The operator trapped in the crane operating console of the exhaust stack was transferred to the ground at 5:13PM and confirmed the death at 5:17PM.

[Thermal Power Station]Hirono Thermal Power Station Units 2 and 4: shutdown due to earthquakeHitachinaka Thermal Power Station Unit 1: shutdown due to earthquakeKashima Thermal Power Station Units 2, 3, 5, 6: shutdown due to earthquakeOhi Thermal Power Station Unit 2: shutdown due to earthquake (Unit 3 resumed operation)Higashi-Ohgishima Thermal Power Station Unit 1: shutdown due to earthquake

Because TEPCO's facilities have been seriously damaged, power shortage may occur. TEPCO appreciates customers' cooperation in reducing electricity usage by avoiding using unnecessary lighting and electrical equipment.

We are taking all measures to restore power, however, we expect extremely difficult situation in power supply for tomorrow as well.We kindly ask our customers to cooperate with us in reducing usage of power.

True, but I’ll bet he just approximated it in his head without whipping out the calculator. I mean, you figure one whole step is 10x, so 0.7 increments is gonna be roughly 7x. And you’re right, it was an excellent article.

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Da Cat

March 13, 2011 23:27

Surely the unwashed masses can trust the pronouncements of our scientific elite. Back in the day they were sending soldiers into ground zero of nuclear explosions without masks, injecting retarded children with plutonium, and doing above ground nuclear tests downwind of civilians.

You can trust a shill for the highly profitable nuclear industry, when we still have nowhere to put the spent fuel which is gathering in storage pools around nuclear reactors, and easy targets for theft or terrorists (it’s already happened at several sites.) Studies done after 9-11 showed a small group of armed terrorists could easily seize control of a reactor control room as sites are lightly guarded.

GMO foods are perfectly safe, plants bred to handle stronger pesticides, and produce them systemically are no problem, and the massive amount of chemicals in breast milk, from pesticides, fire retardants, and plastic containers is nothing to be alarmed about.

You should feel safer that all your phone and Internet communications are being monitored for your own safety., and AI programs can highlight and track language like the above for angry discontents.

Oh Brave New World!

Nothing to see here folks–keep moving right along…

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Charles Bell

March 13, 2011 23:50

The statement “in order to control the nuclear chain reaction, the reactor operators use so-called ‘moderator rods’. ” is incorrect.

Control rods with either Boron or Hafnium are used. Certain isotopes of Boron or Hafnium absorb neutrons. Cadmium has been used in some reactors from the ealriest days.Commercial PWRs borate their core and withdraw control rods. Commerical BWRs use control rods to shape the axial and radial neutron flux.

ILiquid moderator usually is flowing in between fuel and control rods in the core to remover thermal heat..

Some advanced fuel types in BWRs have a water rod (a fuel rod or pin with no fuel in it) to improve moderation in regions of the core where steam void is higher.

N-16 is not a fission product, N-16 or Nitrogen-16 is a radionuclide produced by neutron capture reaction in the core with oxygen-16. (n, p) reaction with16O.

It is the predominat source of radiation in the reactor while it is at power. Its short life on the order of 7 seconds means it quickly decays away after reactor shutdown (when neutron flux drops in tot he source range.

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Helva

March 13, 2011 23:55

What a great article. I wish people would read this instead of watching fear monging tv.

But it was designed for an 8.0 earthquake — and missed that by a magnitude of 7.

If it was designed to withstand an 8.0, and it was hit by a 9.0, then it seems pretty remarkable that it is three days out, there has not been a nuclear explosion and it remains uncertain whether or not there has been a meltdown, even without power at Unit 1.

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Anonymous

March 14, 2011 01:01

The author put a lot of effort into explaining what he thinks is going on in Fukushima, and he’s entitled to his opinion. It annoys me greatly that some people in the comments are attacking the author for not saying what they want to hear.

Of course a lot of this is speculation, but it’s optimistic and hopefully accurate. It almost appears that those people want to be told that it’s all going to blow up. Sounds like they are here to push a political agenda, and that really pisses me off. Shame on you!

For those of you wondering and debating over the author’s background and inherited experience, here’s his publication list. He seems to focus on risk management in global supply chains and lean product development. I don’t know how qualified that makes him to comment on the universals of nuclear plant crises?

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Courtney

March 14, 2011 01:51

Very well written, and much more useful than any media I’ve come across so far. For those picking on the author, he’s got his facts about 90% straight, which is about 90% better than any other information out there that is easily accessible. Thanks for the article!!!

Thanks for the writeup. We needed some sort of filter. It took three of us, retired nuclear engineers with plant licenses, to figure this event out as it was unfolding. Very confusing. The only comment I have is that you infer that the primary system may ok after the sea water injection. The chlorides will attack the stainless steel components and will pose it’s own downstream problems. This was observed in the early 1970’s at Millstone Unit 1.
Another issue not addressed yet is the spent fuel pool integrity and cooling. The spent fuel pool on this unit is at the top of the reactor building, where the top of the building was blown away. This may not be an issue if most of the spent fuel has been reprocessed. What a mess.

This article should be required reading for media types who are reporting on this subject.

I wonder why no one has come up with a steam powered cooling pump. If you have to dump steam in a loss of gravity incedent, at lease get some work out of the deal.

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Anonymous

March 14, 2011 05:25

Always good to hear from a shameless nuclear industry shill.

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Eeyore3061

March 14, 2011 05:35

I’ve got a question.

With the effulent impacting the rotory air impeller, why didn’t someone cut off the non fitting plug and hotwire the trucked in emergency diesel generator set into the buildings wiring?!?

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Rina Liddle

March 14, 2011 05:59

This article reminds me of when scientists were claiming that the Gulf oil spill would be dissipated with chemicals with no harm to the marine life.

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sy

March 14, 2011 06:23

I’d like to see someone explaining these figures. I’m all for nuclear power and I would very much like to believe this article. But these numbers are startling me…

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Anonymous

March 14, 2011 06:34

Linear approximation with something you have gone out of the way to mention uses a logarithmic scale is not a clever plan. Bonus points for bashing errors in the opening then diving in with poor use math.

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Mark Schmidt

March 14, 2011 07:12

Thank you for posting Dr Josef Oehmen’s explanations regarding the accident at Fukushima I nuclear power plant, because it represents one of the finest pieces of propaganda I ever came across in the nuclear industry. He clearly knows how to hide his misrepresentations in a lot of facts. To give a few examples:

“At this point the plant operators begin to follow emergency procedures that are in place for a “loss of cooling event”. It is again a step along the “Depth of Defense” lines. The power to the cooling systems should never have failed completely, but it did, so they “retreat” to the next line of defense. All of this, however shocking it seems to us, is part of the day-to-day training you go through as an operator, right through to managing a core meltdown.“

Well, sounds like just any other working day in Fukushima I. The “loss of cooling event” relates to a loss of regular cooling, where then emergency cooling systems would take over, not to a complete loss of all emergency cooling power, too.Where he is right: The power to the cooling systems including the Emergency Core Cooling System (ECCS) should indeed never have failed. The ECCS is made up of several redundant sytems that can take over and they are not supposed to fail altogether. It is not just a “step along the Depth of Defence line”. With the loss of all emergency cooling capacity the end of the regular defence line was already reached after the battery backup ran out. From there, there is no playing by the book any more. A complete failing of all emergency systems is not part of the “day-to-day training you go through as an operator”. And no-one can teach you to manage a core meltdown, because there are to many variables in such a situation and only limited experience (thank god) exists for such scenarios. They are to be avoided by the operating personnel by all means. The actions taken by the Japanese operators prove that they are experienced and well-trained or the situation would be much worse already, but they are nevertheless improvised and not the result of routine training.

“It was at this stage that people started to talk about core meltdown. Because at the end of the day, if cooling cannot be restored, the core will eventually melt (after hours or days), and the last line of defense, the core catcher and third containment, would come into play.“

To my knowledge the Mark I containment which is installed in Fukushima I block 1 doesn’t include a “core catcher”, so there wouldn’t be any way to securely encase a completely molten reactor core once it has penetrated the reactor pressure vessel. Looks like even the graphic “Figure 20. Mark I General Electric, GE BWR Containment” confirms that.

“The priority now is to maintain integrity of the first containment (keep temperature of the fuel rods below 2200°C), as well as the second containment, the pressure cooker. In order to maintain integrity of the pressure cooker (the second containment), the pressure has to be released from time to time.“

The integrity of his so called first containment, which is not a real containment in the proper sense – the zircalloy encasing pipes of the fuel (uranium oxide) – has obviously at least partially failed, because fission products caesium-137 and iodine-131 could be detected outside the power plant, probably as result of venting to release pressure inside the “pressure cooker”. But it means that at least part of the zircalloy must have melted and flown down the fuel rods exposing the uranium-oxide inside and its fission-products to the surrounding steam. We’re now talking temperatures above 2200 °C. These temperatures are reached only if at least the upper part or the full height of fuel-rods has fallen dry and is merely surrounded by steam which cannot supply sufficient cooling to remove the residual decay heat. If such a situation is not fixed immediately, meaning cooling water cannot be brought into the reactor pressure vessel and be pumped through the reactor core (it has to flow between the fuel rods to cool effectively which can be prevented by molten zircalloy that has flown down the rods blocking the free flow of cooling water) within one to maybe very few hours then there is no chance of preventing further core meltdown because the water simply can’t flow between fuel rods any more. There is no information how far the process in block 1 of Fukushima I had progressed, when TEPCO personnel were able to inject freshwater and boric acid into the reactor pressure vessel. They actually say they were able to bring those coolants inside the core which might suggest that the damage to the fuel rods isn’t too big yet. Let’s hope that.

“The problem is that at the high temperatures that the core had reached at this stage, water molecules can “disassociate” into oxygen and hydrogen – an explosive mixture. And it did explode, outside the third containment, damaging the reactor building around. It was that sort of explosion, but inside the pressure vessel (because it was badly designed and not managed properly by the operators) that lead to the explosion of Chernobyl. This was never a risk at Fukushima. The problem of hydrogen-oxygen formation is one of the biggies when you design a power plant (if you are not Soviet, that is), so the reactor is build and operated in a way it cannot happen inside the containment.“

Of course the formation of oxyhydrogen was and still is a major risk at Fukushima (look at TEPCO statements on their website). Water can and does disassociate and form hydrogen and oxygen inside the pressure vessel, where else would the necessary temperatures be reached for this to happen. Luckily the operators vented the pressure vessel in time before too much of it could build up and explode inside the pressure vessel or the outer steel-reinforced concrete containment. Surely this was and is one of the biggest threats to the reactor during the attemps to cool it down now. It wasn’t just a problem of these “stupid and irresponsible russians in Chernobyl”.

“So the pressure was under control, as steam was vented. Now, if you keep boiling your pot, the problem is that the water level will keep falling and falling. The core is covered by several meters of water in order to allow for some time to pass (hours, days) before it gets exposed.“

According to a member of the German “Strahlenschutzkommission” the core normally is covered by 4 meters of water (the length of a fuel rod) of which only 1.7 meters were left by Friday evening (Don’t know how he came across that data, since neither TEPCO nor the Japanese governement have released any detailed information like that officially). Considering the thermal power it’s certainly not a matter of days before the core falls dry when external cooling stops but of very few hours. So that time must have already run out before the Japanese operators managed to insert new coolant.

“The Plan A had been to restore one of the regular cooling systems to the core. […] But Plan A had failed – cooling systems down or additional clean water unavailable – so Plan B came into effect.“

This so called Plan B is not a plan at all. It merely consists of improvised measures because all provisions to handle critical events in that reactor were lost due to the earthquake (loss of external power supply) and the tsunami (loss of emergency power supply resulting in loss of emergency cooling capacity; maybe loss of or reduced inflow of cooling seawater into the secondary cooling circuit, so maybe no chance of restoring normal cooling within the days and weeks to come even if electrical power supply is restored). A situation that cannot have been included in the risk assessment at the time of construction, because something like that has never happened before and was up to now considered so extremely unlikely, that it was thought of as impossible. (Hence the obvious shock inside the expert community). So it’s certainly not included in any kind of handbook or training for operators of Fukushima I or anywhere else in the world. What the operators are trying to do now is to prevent the worst, i.e. the release of a sigificant percentage or even most of the nuclear inventory of the core (about 60 tons of radioactive material) into the surrounding using their certainly profound knowledge about the construction and operation of their nuclear power plant. So far they have succeded in doing that, but it’s not over yet, not at all.

“In order to prevent a core meltdown, the operators started to use sea water to cool the core. I am not quite sure if they flooded our pressure cooker with it (the second containment), or if they flooded the third containment, immersing the pressure cooker. But that is not relevant for us. The point is that the nuclear fuel has now been cooled down.“

No, it’s not irrelevant whether the coolant went inside or outside the pressure vessel. If they just immersed the “pressure cooker” the nuclear fuel is not cooled down and there is no way to prevent the reactor core inside the “pressure cooker” from completely melting down. The only thing you can hope to achieve by cooling from the outside is to prevent the steel of the “pressure cooker” from melting through or from weakening so much that it cannot withstand the steam pressure and oxyhydrogen explosions inside any more thus releasing its hot and highly radioactive content into the outer containment (a 1.2 – 2.4m thick steel-reinforced concrete hull, don’t know the exact thickness in the Fukushima I plant) that forms the “last line of defense”. Were it to come to that nothing else could be done except to wait and pray. Since there would still be quite a lot of steam and coolant enclosed, they would have to reduce pressure again, probably several times, to protect the concrete hull and to keep at least most of the nuclear material in by releasing radioactive steam now mixed with a considerable amount of long lived fission products into the environment. The melting process could even result in the reactor becoming critical again, that means the nuclear chain reaction in the molten uranium-oxide could start again completely uncontrolled with unforseeable and possibly catastrophic outcome.

“Because the chain reaction has been stopped a long time ago, there is only very little residual heat being produced now. The large amount of cooling water that has been used is sufficient to take up that heat. Because it is a lot of water, the core does not produce sufficient heat any more to produce any significant pressure. Also, boric acid has been added to the seawater. Boric acid is “liquid control rod”. Whatever decay is still going on, the Boron will capture the neutrons and further speed up the cooling down of the core.“

Taking into account the long time the reactor core has been operating continuously there must have been a substantial build-up of fission products, so that the residual heat produced by the fission products of uranium is far from being “little” or there woundn’t have been a cooling problem in the first place (We’re talking of the order of 100MW of thermal power). The residual decay heat would rather lie close to 10% than 3% of the maximum thermal output of the reactor which only slowly decreases over time as the fission products decay. A process that can take weeks or months until the core rods can be handled without the cooling capacity of a fully functional reactor.

Something else that makes me worry:To my knowledge boric acid is usually not used in BWRs. I’m not quite sure why it was mixed to the cooling water that was inserted into the pressure vessel (according to TEPCO). Since the boron acts as a neutron “catcher” it would only reduce the number of neutrons that can split uranium atoms which is already prevented by the insertion of the control rods during the emergency shutdown. It has no influence on the decay of fission products, i.e. on residual heat production. The only explanation I can come up with is that there is already concern that the melting core could become critical again. That would mean the situation is very very serious and the worst is yet to come.

Summing up:It’s an extremely dangerous situation in Fukushima I, nothing anyone can be trained for. What exaclty happened remains unclear. The amount of radioactivity released into the environment seems to be comparatively (to Chernobyl) low so far. It is not at all certain that it stays this way. At least some amount of core meltdown must have occurred. How far the fuel rods in the reactor core have been destroyed remains unclear. The measures undertaken are way out of regular emergency procedures. Whether the meltdown could be stopped remains uncertain. It’s also unclear if the cooling can be sustained, since there still isn’t a stable external power supply. Considering the time it takes until residue decay heat production reaches a “safe” level, it will at least be weeks before anyone can say with certainty that the situation is under control . And now two other blocks of Fukushima I are reported by TEPCO to show similar problems. There has even been report of a hydrogen explosion in block 3 similar to that of block 1. Let’s hope the Japanese operators stay lucky.

Greetings from just another physicist ashamed of the distortions and downplaying of the dangers by Dr Josef Oehmen.

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sseeplane

March 14, 2011 08:55

Actually there is a steam driven cooling pump separate from the normal steam driven feedwater pumps in a BWR. It’s called a Reactor Core Isolation Cooling (RCIC) pump. It can be used for a limited amount of time until there is no useful steam pressure available.

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sseeplane

March 14, 2011 08:55

Actually there is a steam driven cooling pump separate from the normal steam driven feedwater pumps in a BWR. It’s called a Reactor Core Isolation Cooling (RCIC) pump. It can be used for a limited amount of time until there is no useful steam pressure available.

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Anonymous

March 14, 2011 09:58

Nope, 5 is correct. It is logarithmic scale. Which means 10^(8.9-8.2)=5.12.

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Anonymous

March 14, 2011 10:34

While I agree with your sentiment that the people affected are indeed in need of aide, that line you quoted above was written in the context of the supposed “Nuclear Catastrophe” caused by the earthquake and not about the quake itself. He was obviously speaking about the Plant and not the earthquake, nothing callous there.

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Anonymous

March 14, 2011 10:59

I don’t understand a word of what you have written.

Probably why it was written in “layman’s” terms, so those of us who aren’t scientists can understand in a clear way without the media hype.

If I were to go by what the media is telling us, there is going to be a mass melt down sending radiation to all the countries surrounding the pacific ocean.

PS. Thank you to the author

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DavidAKZ

March 14, 2011 12:36

Good one. I don’t think a non fitting electrical coupling is going to stand between you and a core pressure increase !

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Dice

March 14, 2011 16:39

Mark,

Thank you for your insight. You may have heard the recent news that the Fukushima I Block 2 has been exposed without cooling water at all. And it’s completely the operator’s fault, as they didn’t realize the water pump had run out of gas. I’m scared that the core has been exposed with no water for hours, and like your post says, if the core encasing has already melted, cooling it again now wouldn’t be able to prevent further meltdown.

The media in Japan (and the States) have stopped talking for the past few hours, which is freaking me out. What are the possible outcomes from the current situation, and what actions should people living in Japan take? (Get away from Fukushima by at least XX miles, for example)

Thanks,

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Ryan Reed

March 14, 2011 18:31

“Something else that makes me worry:To my knowledge boric acid is usually not used in BWRs. I’m not quite sure why it was mixed to the cooling water that was inserted into the pressure vessel (according to TEPCO). Since the boron acts as a neutron “catcher” it would only reduce the number of neutrons that can split uranium atoms which is already prevented by the insertion of the control rods during the emergency shutdown. It has no influence on the decay of fission products, i.e. on residual heat production. The only explanation I can come up with is that there is already concern that the melting core could become critical again. That would mean the situation is very very serious and the worst is yet to come.”

BWRs do not use boric acid to control fission burn-up, but they most defiantly have them installed for situations exactly like this when the reactor has to be poisoned. All Japanese and American BWRs have boric acid injectors. The use of boron is far more effective at stopping neutron exchange than the control rods. No control rod system exists that can perform as well as boric acid.

Dice,unfortunately I can’t offer you reassuring messages. The news from official sources I’m observing – IAEA and TEPCO – have almost stopped. Not a good sign, I agree. The last statement of the IAEA I saw, regarding the reactors, (14 March 2011 at 15:35 CET) said that they were injecting seawater into the reactor of block 2. It remained unclear whether inside or outside the pressure vessel. TEPCO hasn’t issued any further information. Other news sources in Germany (not necesserily reliable) said that inserting coolant inside failed and the pressure vessel is now just kept immersed in sea water. If that’s true core meltdown will progress in block 2.

What will be the outcome cannot be predicted at the moment.

Please don’t blame the operator for the reported falling dry of the reactor core of block 2, if that can indeed be attributed to human error. Government and media pointing fingers because they don’t know what to do any more, is another very bad sign. All of these operators have been working round the clock for several days now, and have done an incredible job – under enormous physical and psychological stress at the cost of “suffering personal tragedy” (quoting DG of IAEA) – trying to control something that can hardly be controlled. They might even have been fighting a lost cause from the beginning. If you have to blame someone, blame the people who thought it was a good idea to put nuclear power plants in one of the geologically most unstable places in the world, having even the guts to place all of them right at the coastline for convenient cooling by seawater, fully aware of the dangers of tsunamis that accompany many large earthquakes there.

It is still possible that the outside cooling might prevent the reactor pressure vessel in block 2 from completely melting through or bursting. But that depends on a lot of factors that not even the operators themselves can oversee or control any more. As long as they are able to provide cooling by any means, there is still a chance. They have to keep cooling for several half-lives of iodine-131 (half-life ca. 8 days), however, with no more interruptions of cooling, depending on how much iodine-131 there was inside the fuel rods from the beginning of the emergency shutdown, until the molten and resolidified core has reached a stable temperature that no longer poses a threat to the steel of the pressure vessel. That means they have to sustain uninterrupted cooling with sea water for several weeks now. And its unclear if the operators can provide that considering that stable outside power supply has not yet been reported which the governement certainly would do immediately to show some improvement.

Should the reactor pressure vessel melt through or burst, the reinforced concrete containment may or may not be able to contain all of the radioactive material permanently. It may slowly burn through the bottom, it might burst free violently. In the case of a quick significant (much less than a percent would already be an incredible amount of radiation) release of the radioctive content of the core into the surrounding the Fukushima I site would immediately become a death zone, so no personnel would be able to operate there even for short periods of time without risking to become gravely ill within the next days or weeks or even die immediately. I cannot see how cooling of blocks 1 and 3 could be kept up under such circumstances.So if block 2 goes all three will very likely go.

To make matters worse the Director General of IAEA declared at a press conference (14 March 2011 20:30 CET) that block 3 is not fuelled by uranium-oxide alone but from MOX-fuel which consists of a mixture of uranium and plutonium.

So it stays an extremely dangerous situation that has seen no improvements despite all efforts, but still has a very small chance of ending mild.

What can you do, if you are in Japan:To be honest – if you have the means and can get onto an international flight, I would leave the country now at least for a few weeks until it’s clear what becomes of Fukushima. If nothing serious happens, rebuilding infrastucture and economy of Japan will still be a major challenge not to mention the tragic loss of thousends of lives. If you want or have to stay I cannot give you advice on where to go or what to do, because no-one can predict exactly what will happen.

Let’s hope for the best, but prepare for the worst.My feelings are with you and I wish you and all of Japan the best of luck.Mark Schmidt

P.S.: While I’m writing this, a new IAEA-Update reached me (15 March, 00:03 CET):If I’m not gravely mistaken it means that they are preparing for international assistance and support after the release of large amounts of radioactivity. Quote: “The IAEA can offer support in technical areas such as radiation surveys and environmental sampling, medical support, the recovery of missing or misplaced radioactive sources or advice on emergency response [..] In addition, the IAEA is coordinating assistance from Member States through the Response and Assistance Network (RANET). The network consists of nations that can offer specialized assistance after a radiation incident or emergency. Coordination by the IAEA takes place within the framework of the Convention on Assistance in the Case of a Nuclear Accident or Radiological Emergency.”So the IAEA no longer assumes a mild outcome.

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Mark Schmidt

March 15, 2011 02:16

Dear Ryan Reed,

thank you for clearing the boron matter up. Boron poisoning of the reactor core should have rang a bell earlier. Has been a long time, my only excuse.

GreetingsMark Schmidt

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OUGryphon

March 15, 2011 02:47

I did not see anywhere in this article where he said that the control rods moderate or thermalise fast neutrons. Surely you will agree that the control rods moderate the reaction rate – fully inserted stops the reaction, fully withdrawn makes it possible to output maximum power. I will give him the benefit of the doubt that when he says control rods moderate the reaction, he means it in the system output sense, not in the sense of moderating neutron energy which would be incorrect for this reactor type.

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George P. Burdell

March 15, 2011 02:53

Yes, Anonymous, I know how to do antilogs, and when I wrote my comment, I got the same answer both you and the fellow who wrote the original comment got. My point was that the article’s author was just giving an off-the-top-of-the-head linear approximation. You are right, it’s not precise, and in fact a later edition of the article corrected it, but the difference between 5x and 7x, when dealing with magnitudes of this scale, isn’t all that important. I was merely pointing out where the author may have come up with 7x instead of the more accurate 5x. (And FWIW, the USGS has revised the earthquake to a 9.0, which would be closer to 6x.)

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stjohn

March 19, 2011 07:16

Can’t have a nuclear explosion. Totally impossible. Read about how hard it was to make the first bombs. This issue of having a nuclear explosion is probably high on many people’s concerns but nobody talks about it to dispell the fears. Unless the fuel is bomb grade and is contained inside a gun/cannon designed to shoot two fragments together at high velocity…really high velocity and just perfectly timed, the enriched uranium metal will just vaporize into a “dirty” puffbomb. Reactor grade fuel might get pretty hot but nobody is talking about it vaporizing, boiling or burning…just melting. Melting…like slag in a steel crucible. In Chernobyl what burned was the graphite and it burned because it had oxygen available. Not so within a pressure vessel from what I can figure. Besides, the control rods in Fukujima are not graphite and the design of the system is so it produces less heat when it gets hot…the opposite of Chernobyl. Remember, all that is happening is the buildup of residual heat not the generation of new. When the reactor was shut down…power decreased radically and the production of radiation/fissionable material decreases even more radically when all there is is residual heat.